Interleukin-4 (IL-4) is a cytokine which has many biological and immunoregulatory functions and is released from T-helper 2 (Th2) lymphocytes, eosinophils, and mast cells. IL-4 receptors are found on normal T lymphocytes, B lymphocytes and CD34 myelocytes (Nelms, Annu Rev Immunol, 1999; 17:701-738 ). A functional IL-4 receptor is composed of two transmembrane proteins. The IL-4Rα chain binds IL-4, leading to dimerization with either the IL-2 receptor gamma chain (γC) or with the IL-13 receptor α1 chain to form the type I or type II receptor complexes, respectively. IL-4 engagement of IL-4R results in the phosphorylation of intracellular Janus kinase. The phosphorylated kinase phosphorylates and activates STAT6, which in turn dimerizes and is subsequently translocated to the nucleus wherein the STAT6 promotes transcription of target genes associated with IL-4, inducing inflammation. In a second way, occupation of the IL-4 receptor by IL-4 induce the Janus kinase-mediated AKT/PKB, resulting in increasing cell survival (Nelms et al., Annu Rev Immunol, 1999; 17:701-738). IL-4 also functions to induce the differentiation of naive T-helper (Th) cells to Th2 lymphocytes and the production of cytokines such as IL-4, IL-5, IL-9 and IL-13. Also, IL-4 induces B-cell class switching to IgE (immunoglobulin E). Particularly, IL-4 is implicated in mucin gene expression and mucous hypersecretion, which are features in the pathogenesis of asthma, thus playing an important role in airway obstruction and inflammation (Paul, Blood, 1991; 77:1859-1870). As such, IL-4 is a key regulator in allergic inflammatory response. Accordingly, the proper inhibition of the functions of IL-4 may be appropriate for the treatment of allergic diseases.
In addition, higher levels of IL-4 are found in various cancer tissues than in normal tissues and it is produced in a large amount in tumor-infiltrating lymphocytes (TILs) (Shurin, Springer Semin Immunopathol, 1999; 21:339). IL-4 endows chronic lymphocytic leukemia B cells with resistance to apoptotic cell death (Dancescu, J Exp Med, 1992; 176:1319). Recent reports have exhibited that IL-4 is synthesized in tumor cells and cancer stem cells and binds to the IL-4 receptor on cancer cells to make the cancer cells resistant to apoptosis (Todaro, Cell Death Differ, 2008; 15:762-772; Todaro, Cell Stem Cell, 2007, 1:389-402). The expression level of IL-4 receptors in various cancer cells including non-small cell lung cancer, encephaloma, breast cancer, bladder cancer, pancreatic cancer, prostate cancer, kidney cancer, and Kaposi's sarcoma is much higher than normal cells. In consideration of the acquisition of anticancer agent resistance thereby and the overexpression thereof in cancer cells, the IL-4 receptor may be a promising target for cancer therapy. A fusion protein in which modified IL-4 is fused to pseudomonas toxin is reported to target cancer cells so that the toxin is introduced into the cancer cells to kill them (Joshi, Cancer Res, 2001: 61:8058-8061; Garland, J Immunother, 2005: 28:376-381; Kioi, Cancer Res, 2005: 65:8388-8396; Kawakami, Clin Cancer Res, 2002:8:3503-3511).
Meanwhile, a variety of IL-4 antagonists have been developed as therapeutics for asthma. For example, Immunex Corp. produced Nuvance™, a soluble form of IL-4 receptor, which advanced to clinical trial, but its development was halted due to insufficient therapeutic effects. Pascolizumab, a monoclonal antibody to IL-4, developed by Glaxosmithkline, underwent a clinical trial, but underwent no further development. Bayer developed Pitrakinra, a dual IL-4/IL-13 antagonist in clinical trial studies for the potential treatment of asthma. Sunesis Pharm. Inc developed triphenyl compounds as IL-4 antagonists in clinical trials (WO 2001/098245).
In conventional chemotherapy, anticancer agents, after being administered orally or by injection, are intended to be maintained at a desired concentration in vivo to exert a pharmaceutical effect on an affected site in need thereof, but they affect normal sites as well, incurring side effects. To overcome this drawback, increasing attention has been paid to a drug delivery system capable of delivering drugs selectively to affected sites, or a target therapy which can increase pharmaceutical efficacy even at low dosages accompanied by the concomitant great decrease of side effects in normal tissue.
Generally, a target-aiming drug delivery system is composed of three parts: a soluble polymeric carrier for carrying a drug; a target moiety for allowing a drug to react with a target site; and a spacer for bio-conjugating the drug to the polymeric carrier. In this structure, the drug delivery system enjoys the advantage of increasing lipid-soluble drugs in water solubility, stabilizing the conformation of protein or peptide drugs and reducing side effects or multidrug resistance for anticancer agents. Particularly, the target moiety guides the selective reaction of the drug with target cells or tissues, so that the system is applicable even to small-size tumors in the early stage, thus effectively treating diseases.
A liposome is a spherical vesicle composed of a lipid bilayer. The lipid bilayer is made mostly of phospholipids which are amphiphilic with a hydrophilic phosphate head and two hydrophobic lipid tails. When exposed to an aqueous phase, phospholipids arrange themselves into a bilayer which may form a closed structure like a cell. In the bilayer structure, the hydrophobic lipid tails face inside with the hydrophilic head facing outside. The major types of liposomes are the multilamellar vesicle and the unilamellar vesicle. Unilamellar liposomes have single lipid bilayers while multilamellar liposomes contain two or more lipid bilayers. Liposomes may be prepared by various methods [Cullis et al., in: Liposomes, From Biophysics to Therapeutics (M. J. Ostro, ed.), Marcel Dekker, pp. 39-72(1987)].
Because they are delivered selectively to an affected site, a drug loaded into a liposome has decreased side effects and increased pharmaceutical efficacy. In addition, liposomes are typically captured by phagocytic cells of the reticuloendothelial system in the capillaries so that the loaded drug is released directly into the intracellular infected site.
An anticancer agent-loaded liposome labeled with an IL-4 receptor-targeting peptide can be used as a drug carrier that delivers the drug selectively to the cancer tissue of interest. Therefore, the IL-4 receptor is thought to be useful as a smart drug carrier for cancer therapy.